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Heavy Quark Suppression at RHIC Magdalena Djordjevic Columbia University

Heavy Quark Suppression at RHIC Magdalena Djordjevic Columbia University. Motivation for studying heavy quarks Heavy quark energy loss What is the heavy quark and single electron suppression at RHIC? Conclusion.

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Heavy Quark Suppression at RHIC Magdalena Djordjevic Columbia University

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  1. Heavy Quark Suppression at RHIC Magdalena Djordjevic Columbia University

  2. Motivation for studying heavy quarks • Heavy quark energy loss • What is the heavy quark and single electron suppression at RHIC? • Conclusion

  3. One of the central questions in high energy heavy ion physics is whether a quark-gluon Plasma (QGP) has been discovered at RHIC.(M.Gyulassy and L. McLerran, nucl-th/0405013, M.Gyulassy, nucl-th/0403032) • Collective Flow and Jet Quenching of light partons strongly suggest that QGP is discovered. • Further detailed tests of jet tomography using heavy quarks could be decisive as a complementary test of the theory. Open charm suppression, which can now be measured at RHIC by comparing pt distributions of D-mesons in D-Au and Au-Au collisions, is a novel probe of QGP dynamics.

  4. What value of heavy quark suppression we can expect at RHIC? 1997 Shuryakproposed that charm quarks will have large energy loss in QGP => large suppression of D mesons. 2001 Dokshitzer and Kharzeev proposed “dead cone” effect => charm quark smallenergy loss

  5. First Au+Au->e X data show no hint of heavy quark energy loss ! ?? PHENIX Collaboration (K. Adcox et al.) Phys.Rev.Lett.88:192303,2002 RAA(pT) for non-photonic single electrons in Au+Au !Significant reduction at high pT suggest sizable energy loss! Sergey Butsyk (21st Winter Workshop on Nuclear Dynamics)

  6. What we wanted to do? We wanted to compute quantitatively radiative energy loss for heavy quarks including dielectric and collision sources. Why? To present theoretical predictions that can be compared with upcoming experimental results in order to test the QGP theory.

  7. Radiative heavy quark energy loss • There are three important medium effects that control the • radiative energy loss at RHICand LHC. • Ter-Mikayelian effect(M. Djordjevic, M. Gyulassy, Phys.Rev.C68:034914,2003) • Transition radiation(B.G. Zakharov, JETP Lett.76:201-205,2002) • Energy loss due to the interaction with the medium (M. Djordjevic, M. Gyulassy Nucl.Phys.A 733, 265 (04)). 1) 2) 3)

  8. Energy loss due to the interaction with the medium The most important effect is the induced gluon radiation caused by the multiple interactions of partons in the medium. To compute medium induced radiative energy loss for heavy quarks we extend Gyulassy-Levai-Vitev (GLV) method, by introducing both quark M and gluon mass mg.

  9. + + This leads to the computation of the fallowing types of diagrams: To compute energy loss to all orders in opacity we apply algebraic recursive method described in (GLV,Nucl.Phys.B594(01)).

  10. We generalized GLV Opacity Series (NPB594(01)) to MQ and mg > 0 (DG, Nucl.Phys.A 733, 265 (04)) Hard, Gunion-Bertsch, and Cascade ampl. in GLV generalized to finite M

  11. The numerical results for induced radiative energy loss are shown for first order in opacity, with assumed opacity of 5 fm.

  12. For 10 GeV heavy quark (c, b) jet, thickness dependence is close to linearBethe-Heitler like form L1. This is different than the asymptotic energy quadratic form characteristic for light quarks.

  13. How important is the “dead cone effect” for the heavy quark energy loss? light

  14. As the jet energy increasescharm and light quark energy loss become more similar, while bottom quark remains significantly different. For 5 GeV heavy quark (c, b) jet, thickness dependence is closer to linearBethe-Heitler like form L1, while light quarks are closer to quadratic form. As the jet energy increases, the dead cone effect becomes less important.

  15. D, B c, b 1) production 2) medium energy loss 3) fragmentation D and B meson suppression To make theoretical predictions for D and B meson pt distributions we used GLV method described in PLB538:282-288,2002. To apply this method we need to know: 1) Initial pt distribution of heavy quarks 2) Difference between medium and vacuum heavy quark energy loss 3) D and B meson fragmentation function.

  16. <kt2>=0 Initial heavy quark pt distributions To compute the initial charm and beauty pt distributions we applied the MNR code (Nucl.Phys.B 373, 295 (1992)), and used the same parameters as in Vogt’s paper (Int.J.Mod.Phys.E 12,211(2003)).

  17. Heavy quark suppression as a function of pt M. Djordjevic, M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005)

  18. light Comparison with pion suppression

  19. Initial Charm and Beauty pt distributions Charm and Beauty pt distributions in p+p Charm and Beauty pt distributions in Au+Au

  20. Single electrons Panels show single e- from MNR (done by R.Vogt). Red curves show total single e-; Blue (green) curves show contribution from Charm (Beauty). Beauty dominate the single e-spectrum after 4.5 GeV!

  21. Raa for single e- Red solid curve: Raa for non-photonic single e-. Blue (Green)dashed curves: Raa for single e- from Charm (Beauty) quarks. MNR Wepredictsmall single e- suppressionof ~ 0.7

  22. Comparison with experiment Our predictions do not agree with PHENIX preliminary data

  23. How to explain this puzzle? PHENIX preliminary data suggest single electron suppression similar to pion suppression! • From the current model this would be hard to explain because of: • Bottom contribution to single electrons • Gluon contribution to pions Therefore, to explain the data, we need a model which would eliminate bottom contribution from single electrons + eliminate gluon contribution from pions!

  24. Problems with single electrons I No centrality dependence Factor of 2 suppression?

  25. Consistency between electron data sets • STAR systematically (slightly) above PHENIX • beware: error bars are meant to be takenseriously! (Slide adapted from Xin Dong, 21st Winter Workshop on Nuclear Dynamics) Single electron results can be different by an order of magnitude Maybe single electrons are not good probe of Heavy quark energy loss?

  26. Problems with single electrons II Charm and beauty content in the single electrons is very sensitive to their fragmentation functions Single electrons suppressionis strongly dependenton(unknown) charm and beauty fragmentation functions MNR Simon Wicks (Columbia U.)

  27. Single electron distributions are VERY sensitive to the rapidity window (Ramona Vogt) + At high rapidity, nonperturbative effects may become important! Single electron suppression could be influenced by nonpertutbative effects For example for RHIC we should include heavy quarks up to |ymax|=2.5. We need D mesons! For LHC |ymax| could be significantly larger than 3!

  28. Conclusions D meson data for 200 GeV D-Au and Au-Au results, should soon become available from STAR. We predict moderate D meson suppression ~ 0.50.1 at RHIC. At the moment, we are not able to explain PHENIX results, but we are searching for possible solutions! However, single electrons may not be a good probe of heavy quark energy loss. We need an accurate measurement of D mesons!

  29. Backup slides

  30. Ter-Mikayelian effect This is the non-abelian analog of the well known dielectric plasmon effect w(k) >wpl~ gT In pQCD vacuum gluons are massless and transversely polarized. However, in a medium the gluon propagator has both transverse and longitudinal polarization parts. We extended the work of Kampfer-Pavlenko (2000) to compute both longitudinal and transverse contributions to the 0th order in opacity. The Ter-Mikayelian effect on QCD Radiative Energy Loss M. Djordjevic, M. Gyulassy, Phys.Rev.C68:034914,2003

  31. In order to compute the main order radiative energy loss we have to compute |Mrad|2, where Mradis given by Feynman diagram: To compute this, we have used optical theorem, i.e.: Where M is the amplitude of the fallowing diagram: Dielectric Effect

  32. Comparison between medium and vacuum 0th order in opacity fractional energy loss is shown on the Fig.1: CHARM • Longitudinal contribution is negligible. • The Ter-Mikayelian effect on transverse contribution is important, since for charm it leads to ~30% suppression of the vacuum radiation. The Ter-Mikayelian effect thus tends to enhancethe yield of high pT charm quarks relative to the vacuum case.

  33. Fig.2 shows the one loop transverse plasmon mass mg(k)√(2-k2). We see that mgstarts with the value pl=µ/√3 at low k, and that as k grows, mgasymptotically approaches the value of m=µ/√2, in agreement with Rebhan A, Lect. Notes Phys. 583, 161 (2002). We can conclude that we can approximate the Ter-Mikayelian effect by simply taking mg m .

  34. Transition radiation An additional dielectric effect at 0th order in opacity. It must be taken into account if the QGP has finite size. Transition radiation occurs at the boundary between medium and the vacuum.

  35. To estimate transition radiation we follow Zakharov (B.G. Zakharov,JETP Lett.76:201-205,2002). This computation was performed assuming a static medium.

  36. Can this energy loss be smaller in the medium than in the vacuum? Transition radiation lowers Ter-Mikayelian effect from 30% to 15%.

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